What Is a Wound Vac?

Wound care often requires bandages, dressings, medical tape, and antiseptic solutions. However, complex wounds might require much more. Difficult wounds can postpone healing and cause pain while simultaneously imposing a significant financial and social burden. In those cases, non-conventional methods, like a wound vac, may be implemented to promote wound healing and improve patient outcomes. 

If you’re not really sure what a wound vac is or simply want to brush up on your skills, this is the perfect resource for you. Below, we’ll answer questions like what is a wound vac and how does it work, what’s is a wound vac’s purpose, and more! 

So What Is a Wound Vac? 

While often referred to as wound VAC, the abbreviation actually stands for vacuum-assisted closure. You might also hear it called negative pressure wound therapy, or NPWT, for short. This non-surgical medical treatment encourages wound healing by applying negative pressure evenly across the entirety of the wound site.  

The U.S. Food and Drug Administration (FDA) classifies NPWT systems as a class II medical device, meaning it presents a moderate risk to patients and users. You can also find blood pressure cuffs and glucose meters in the same class. 

The Wound Vac Design

In order to achieve subatmospheric pressure to promote wound healing, the right materials have to be in place. The vac therapy wound dressing system includes the following:  

• Polyurethane foam sponge  
• Semiocclusive adhesive cover
• Fluid collection system
• Suction pump 

The foam sponge contains pores that are around 400 to 800 micrometers and is meant to be trimmed according to the wound’s size. Once cut, it should be set on top of the wound as it helps ensure that the wound’s surface is equally exposed to the negative pressure. Following that, the transparent adhesive cover should be applied to the entire area, covering the wound and foam. Wound care specialists will want to ensure the adhesive cover sticks tightly to the healthy skin surrounding the wound, as it helps to stop air penetration, and creates a partial vacuum in the wound. 

The fluid collection system, which consists of a drainage tube anchored under the adhesive cover, is attached to the vacuum pump. Together, they siphon wound interstitial fluids, bacteria, and other substances through the foam. From there, the exudate and more will be collected in a tank and later disposed.

The NPWT system may perform this action continuously or intermittently. Research suggests that intermittent VAC therapy may be better for conditions like diabetic leg ulcers, as it led to marginally more closure rates than those in the continuous group. 

Types of Wound Vac Systems: Single-Use vs. Traditional

All wound vac devices use a pump to reduce pressure and have the same general design and function but may have different features. Some might be powered electronically or be battery-operated. They might also have different pressure range settings, which are programmed by wound care specialists based on the ideal pressure to treat each specific wound type. Today, most NPWT devices have a pressure setting range between -40mmHg and -200mmHg. 

Some wound vac devices are disposable and can only be used by one person. Single-use NPWT (sNPWT) devices are compact, making them suitable for active patients in home care settings with minimal wound drainage. 

Due to their larger pump, traditional NPWT (tNPWT) devices can collect large volumes of wound drainage. They’re specially designed for many years of use with several patients. 

Both types of NPWT devices are beneficial, but there’s some evidence that sNPWT devices may lead to better patient outcomes in some situations. For example, one study discovered that patients with chronic leg ulcers utilizing a sNPWT device experienced quicker wound closure and fewer adverse events during treatment.

What Is the Purpose of a Wound Vac?

Although the purpose of wound vacs has evolved over the years, the overarching goal remains the same: to help heal wounds. To better understand this, let’s examine their history. 

A Brief History of Wound Vacs

In 1993, Fleischmann et al introduced the idea of using controlled subatmospheric pressure to treat open or infected wounds. Although we can’t feel it, atmospheric pressure, also known as the gas in the air, is constantly exerting pressure on the body. If a wound is present, having these air molecules colliding with the body can interfere with healing.

To aid with this, the researchers developed a vacuum-sealed dressing to encourage the healing of open fracture wounds in injured patients. Additional studies explained how negative pressure dressings could help treat acute and chronic infected wounds and fasciotomy wounds on the lower extremity.

Later, Michael Morykwas and Louis Argenta utilized foam dressing and a vacuum pump to manage wounds. This design allowed them to adjust the vacuum’s pressure and determine whether they preferred continuous or intermittent therapy.

They observed that removing the atmospheric pressure over the area using this device enhanced wound healing physiology by decreasing inflammatory exudate and encouraging granulation tissue. By 1997, the wound vac device was popularized as an innovation designed to enhance secondary intention wound healing. 

Today, NPWTs are most often used for non-healing complex wounds or those at risk of becoming chronic wounds.

The Purpose of Wound Vacs for Acute Wounds

A medical professional may add a wound vac to a patient’s treatment plan if they have an acute wound that can’t be closed by primary intention (i.e. bringing the wound edges together with staples, glue, or sutures, to close it). This might be due to swelling, skin tension, an active infection, or the patient’s risk of infection.  

Consider this:  traumatic wounds, such as open lacerations, open fractures, burns, and degloving injuries, are at an increased risk of infection due to potential contamination of the surrounding environment or the injury itself. Skin grafting or primary closure aren’t the best approach with these wound types because microorganisms could become trapped in the soft tissue. This may cause abscesses to form and eventually lead to tissue death. 

Introducing a wound vac places the acute injury in an environment where tissue growth is stimulated and wound apposition is probable. 

Negative Pressure Therapy for Chronic Wounds

Characterized by their physiological impairment and delayed healing time, chronic wounds require very careful care. Evidence shows that NPWT for these types of wounds has resulted in more significant wound size reduction than standard treatment. They’ve also found that healing time is shorter, taking 29 days compared to 45 days of standard wound care. 

Wound vac therapy decreases the preparation stage of wound treatment (time between surgical debridement and skin graft application) as well, requiring only seven days. It took 17 days for the control group. Lastly, it was found that wound vac treatment is much more cost-effective than traditional techniques. Given the benefit to patient care and the cost savings, we can say that NPWT serves many purposes for chronic wounds. 

The Role of NPWTs in Wound Separation 

Wound vacs are a solution for preventing or aiding with surgical wound dehiscence as well because they help protect the wound bed. It aids in reviving the skin, thus increasing the likelihood of future wound closure. 

A VAC device may also be implemented to create a healthy wound bed for successful skin graft application. The wound vac’s ability to decrease edema and seroma formation and encourage granulation to promote healing is invaluable.

How Do Wound Vacs Aid in Wound Healing?

While we know that negative pressure provides an ideal environment for a wound to heal, that doesn’t fully explain what’s happening on a biological level. 

When it comes to wound vacs, it’s crucial to recognize that there are four main mechanisms of action, which are: 

• Macro-deformation 
• Drainage of fluids 
• Stabilization of the wound environment 
• Microdeformation 

Now, let’s dig in to each one of these mechanisms.

Macro-deformation

Also called wound contraction, the foam sponge decreases in volume by almost 80% when exposed to 125 mmHg of subatmospheric pressure. The sponge should be tautly attached to the wound edges. As it shrinks, the foam’s contact with the skin causes the wound surface to draw together and reduce, too. 

Simultaneously, the peri-wound skin is being remodeled to properly extend. The increased extracellular pressure from macro-deformation promotes tissue compression and granulation tissue formulation. 

Drainage of Fluids

Edema hinders the healing process, so wound care providers do everything they can to decrease it and provide a stable wound environment. It’s believed that swelling may cause compression of cells within the extracellular matrix, thereby reducing their intrinsic tension, and causing a diminished proliferative response. 

A wound vac device applies suction to help evacuate excess fluids and decrease edema. The fluid movement caused by the suction creates shear forces on the cell and ions, creating electric fields. These processes encourage a cellular proliferation reaction, which, as we mentioned before, swelling can limit. 

The removal of extracellular fluid also releases the pressure caused by fluid accumulation around the small blood vessels. This boosts blood flow to the wound, allowing it to receive the nutrients it needs to begin healing. 

The suction draws out toxic materials, like TNF-α and matrix metalloproteases (MMP) as well.

Stabilization of the Wound Environment

The wound vac system includes a semiocclusive adhesive cover that has restricted permeability to water vapor and gases. This provides thermal insulation and warmth to the wound, resulting in a moist environment that’s conducive for healing. 

Even further, the foam sponge is impermeable to microorganisms and proteins, halting bacterial colonization. 

Wound vac therapy requires fewer dressing changes as well. Typically, changes take place every two to three days. The dressings also maintain oncotic and osmotic gradients at the wound surface, allowing it to maintain stability. This moister environment encourages angiogenesis and the breakdown of necrotic tissues while alleviating pain for the patient. 

Traditional wound treatment involves changing the gauze-based dressing daily, which may evaporate fluids and proteins at the wound surface. This could eventually develop a scab that delays healing. We also can’t ignore the fact that these more frequent changes cause greater discomfort for the patient. 

Micro-deformation

The application of mechanical loading leads to deformation forces on the cells, which researchers say “promote cellular proliferation, angiogenesis, and granulation tissue formation.” 

The negative pressure brought on by the VAC device interferes with the integrin bridges (receptors that function as bridges between cells and the extracellular matrix), and releases intracellular messengers. This process changes gene transcription and causes cellular proliferation. 

Studies show that the integrins link to the plasma membrane and actin fibres in the cell cytoskeleton, causing cellular mechanotransduction. This is explained as the process by which “cells convert a mechanical deformation signal into a biochemical or biological response.” 

The application of negative pressure from the VAC device ultimately causes tissue expansion due to the difference in pressure within compared to outside the cells. This is believed to cause cell expansion and the pulling of wound edges closer together to decrease wound size. 

Wound Vac Best Practices

NPWT can be very beneficial, but its success is based on proper use and understanding of how it works. Practitioners should ensure they complete a thorough wound assessment prior to treatment to ensure it doesn’t cause a patient harm. Some patients, depending on their overall health and comorbidities, may not make a good fit for negative pressure therapy. 

The specific characteristics of the wound play a role too, as there are certain scenarios where a wound vac may not be appropriate. For instance, if vital structures are exposed, like blood vessels and organs, NPWT could cause hemorrhage, erosion, or fistulation. In addition, using a wound vac in the presence of a malignancy could lead to the accumulation of genetic mutations within cells, known as tumorigenesis. Malignant tissue will have to be removed prior to considering NPWT. 

Additional considerations include: 

• Infected tissue 
• Weakened/fragile skin 
• Ischemic tissue 

The Future of Wound Vacs is Promising

While NPWT systems have come a long way, there are continually new techniques, wound dressings, suction tubes, and more being created to help produce even more promising results. 

Two examples of NPWT advancements include: 

• NPWT with Instillation. This involves the standard wound vac system combined with an intermittent delivery of a topical solution into the wound bed. 
• Closed Incision Negative-Pressure Therapy (ciNPT). The VAC device is placed in the operating room and provides continuous negative pressure at -125 mm Hg over a primary closed surgical wound. It’s meant to improve wound healing and decrease its vulnerability to complications. 

It’s also expected that new tissue engineering and regenerative medicine modalities could be used in future wound vac systems. We imagine negative pressure therapy will become more personalized to the patient, especially with artificial intelligence on the rise. 

Wound Vacs: A Transformative Tool for Wound Healing

As discussed above, wound vacs have become an instrumental tool in wound healing. Not only do they aid with wound closure, but they also speed up the healing process. Their effect is undeniably profound, especially when you think about the impact wounds, particularly chronic ones, can have on a patient’s quality of life. This beneficial innovation allows practitioners to take better care of their patients, while also reducing the financial woes wounds can have on stakeholders.